RECOMBINANT MICROTUBULE-ASSOCIATED PROTEIN 2C REDUCES THE DYNAMIC INSTABILITY OF INDIVIDUAL MICROTUBULES

The effects of purified recombinant microtubule-associated protein 2c (rMAP2c) on the dynamic instability of microtubules were examined by d irect observation of individual microtubules irt vitro by video-enhanc ed differential interference contrast light microscopy. Microtubules w ere grown in the absence or presence of varying concentrations of rMAP 2c and were analyzed to determine growth rates, shortening rates, and the frequencies of conversion between growing and shortening phases. W e found rMAP2c to stabilize microtubules dramatically. The most notabl e effect is a reduction in both the frequency of catastrophes (transit ions from growth to shortening) and the mean length of shortening even ts: no microtubule catastrophes were observed at concentrations of rMA P2c as low as 1.06 mu M in a solution of 10 mu M tubulin. Even at lowe r rMAP2c concentrations, there is a marked stabilizing effect. As the concentration of rMAP2c increases, average growth rates increase sligh tly, shortening rates decrease, and the frequency of rescues (transiti ons from shortening to growth) increases significantly. Together, thes e changes in parameters produce a population of extremely stable micro tubules in the presence of rMAP2c. This stabilization is consistent wi th a structural role for MAP2c during early postnatal neural developme nt.